The
official residence of British Prime Ministers is number 10 Downing
Street. It is in a side-street off Whitehall, near the Houses of
Parliament.

It
was built by Sir George Downing in 1680, and in 1738 George II offered it to
Sir Robert Walpole, who was Britain's first Prime Minister. The house
can only be opened from the inside, no matter how a person ransack it.
But of course, there is always a guard on standby.